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October 2006
The high cost of fire, both emotional and financial, is well documented, but a study by Monash environmental scientists is assessing the immediate and long-term impact of savanna fires on Australia's climate.
Flying over northern Australia on his way to field work in Cape York, the Top End and Indonesia, Professor Nigel Tapper couldn't help but notice the fires blazing across the tropical savannas below.
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Dr Jason Beringer.
Images courtesy of Dr Beringer. |
As he looked down at the massive fires, he was intrigued by the changing nature of the landscape and began thinking about their possible impact on Australia's climate.
The experience was the catalyst for a major new research project managed by Professor Tapper, who is head of Monash's School of Geography and Environmental Science, and Dr Jason Beringer, also from the School of Geography and Environ-mental Science, within the Faculty of Arts.
The project - 'Impact of fire on surface heat and moisture fluxes in Australian tropical savanna and feedbacks to regional climate' - was a natural progression for Professor Tapper, who became interested in fire and climate interactions while undertaking studies into air quality in major Indonesian cities during the late 1980s and early 1990s.
"The fires blacken the landscape so that it absorbs more of the sun's energy, the process known as solar radiation, and the vegetation stops emitting water, or transpiring," he says. "Even large trees, after a fire has gone underneath them, drop their leaves immediately, whether or not the trees themselves have been burned.
"As a result, the fire turns off trans-piration, and that, combined with the excess solar radiation and the blackened surface, results in more heat being produced above the surface.
"It's of great interest to us to see what effect that heat will have. Flying over northern Australia and looking down at those fires that day, I realised that up to 40 to 50 per cent of northern Australia would be affected in any one year, and that must have a major impact on the climate."
Preliminary results have shown exactly what Professor Tapper and his research team suspected: that after fire, there is a dramatic increase in solar radiation absorbed at the earth's surface, and instead of energy being used to evaporate water, it is used to heat the atmosphere.
This leads to a dramatic shift in local climate and a significant heating of the air immediately above the area of the fire scar.
What Professor Tapper and his team would now like to determine is whether these changes are having just a localised effect or a broader, regional impact.
"The impact of the fire scars - dark areas where, after the fire dies away, the landscape is converted from savanna grassland to dark stumps and ash - may just be in changing local levels of precipitation," Professor Tapper said. "However, on a broad scale it could have the potential to change the strength of the monsoon.
"This is what we want to investigate, to determine the overall impact on the climate." The research team, which includes Monash Centre for Dynamical Meteorology and Oceanography director Dr Steven Siems, Dr Lindsay Hutley from Northern Territory University and Professor Amanda Lynch from the University of Colorado, has been working on the project for the past 18 months and recently received an ARC Discovery Grant to continue the study. Further funds are being sought from the US to broaden the work.
This year, the team will assess the increased heat caused by fire scars and aim to determine the extent to which the atmosphere is heated.
The researchers will use tethered balloons - inflatable devices about the size of a small car, filled with helium, that carry a package of instruments underneath - to measure temperature, humidity, air pressure and wind speed and direction at heights up to two kilometres.Profiles will be taken over varying surfaces and then compared, Dr Beringer says.
"You can imagine that the profile over one surface will be quite different compared to the profile over another. What we expect is that over the fire scars the air will be much warmer and drier to a deeper level than over the unburned savanna.
"When you have those sorts of differences, you have the potential for pressure variation across the surfaces which, under the right conditions, could result in cloud development and precipitation over one surface at the expense of other surfaces. Indigenous Australians have observed storms over late-season fire scars."
Savanna ecosystems account for just over 11 per cent of the global landscape and when they burn, they consume three times more dry matter per year than the burning of tropical forests. For this reason, fires in savannas can have massive impact on regional water, energy and carbon dioxide exchanges, says Dr Beringer, and as a result are likely to have important feedbacks to the atmosphere and regional climate.
"Large-scale burning releases vast quantities of carbon dioxide into the atmosphere that can enhance global warming. We are interested in how much is being released and how much is absorbed back into the vegetation when it regrows after a fire. The overall balance is fundamental to determining Australia's contribution to carbon dioxide emissions," he says.
"As well, the time of the year in which the fire occurs can result in either a stable or dynamic change in vegetation composition and structure over longer periods of time, which in turn can feed back to affect the atmosphere through changes in land surface properties.
"Most of these impacts are not well understood, but it is the goal of this study to understand the processes involved in burning and to determine the broader impact on the environment."
Action
For more information, contact Professor Nigel Tapper on +61 3 9905 2931 or visit www.arts.monash.edu.au /ges/research/climate. | 
